Multiphase compositions for oxidation protection of composite articles

ABSTRACT

The present disclosure includes carbon-carbon composite articles having multiphase glass oxidation protection coatings for limiting thermal and/or catalytic oxidation reactions and methods for applying multiphase glass oxidation protection coatings to carbon-carbon composite articles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of, and claims priority to and thebenefit of, U.S. application Ser. No. 14/671,430, entitled “MULTIPHASECOMPOSITIONS FOR OXIDATION PROTECTION OF COMPOSITE ARTICLES,” filed onMar. 27, 2015, which is incorporated herein in its entirety.

FIELD OF INVENTION

The present disclosure related generally to carbon-carbon compositesand, more specifically, to multiphase oxidation protection systems forcarbon-carbon composite components.

BACKGROUND OF THE INVENTION

Oxidation protection systems for carbon-carbon composites are typicallydesigned to minimize loss of carbon material due to oxidation atoperating conditions, which include temperatures as high as 900° C.(1652° F.). Phosphate-based oxidation protection systems may reduceinfiltration of oxygen and oxidation catalysts into the composite.However, despite the use of such oxidation protection systems,significant oxidation of the carbon-carbon composites may still occurduring operation of components such as, for example, aircraft brakingsystems.

SUMMARY OF THE INVENTION

An article in accordance with various embodiments may comprise acarbon-carbon composite structure and a multiphase oxidation protectioncomposition including a first glass phase and a second glass phase on anouter surface of the carbon-carbon composite structure, wherein thefirst glass phase comprises a phosphate glass composition having a firsttransition temperature, and wherein the second glass phase comprises asecond transition temperature higher than the first transitiontemperature. The second transition temperature may be at least 100° C.higher than the first transition temperature. The second glass phase maycomprise a sealing glass. The first glass phase may be represented bythe formula a(A′₂O)_(x)(P₂O₅)_(y1)b(G_(f)O)_(y2)c(A″O)_(z): A′ isselected from: lithium, sodium, potassium, rubidium, cesium, andmixtures thereof; G_(f) is selected from: boron, silicon, sulfur,germanium, arsenic, antimony, and mixtures thereof; A″ is selected from:vanadium, aluminum, tin, titanium, chromium, manganese, iron, cobalt,nickel, copper, mercury, zinc, thulium, lead, zirconium, lanthanum,cerium, praseodymium, neodymium, samarium, europium, gadolinium,terbium, dysprosium, holmium, erbium, thulium, ytterbium, actinium,thorium, uranium, yttrium, gallium, magnesium, calcium, strontium,barium, tin, bismuth, cadmium, and mixtures thereof; a is a number inthe range from 1 to about 5; b is a number in the range from 0 to about10; c is a number in the range from 0 to about 30; x is a number in therange from about 0.050 to about 0.500; y₁ is a number in the range fromabout 0.040 to about 0.950; y₂ is a number in the range from 0 to about0.20; and z is a number in the range from about 0.01 to about 0.5;(x+y₁+y₂+z)=1; and x<(y₁+y₂). The first glass phase may comprise betweenabout 5 mol % and about 15 mol % of ammonium dihydrogen phosphate. Themultiphase oxidation protection composition may comprise between about1% by weight and about 15% by weight of the second glass phase. Thearticle may comprise a component of an aircraft wheel braking assembly.

A method for limiting oxidation in a composite structure in accordancewith various embodiments may comprise mixing a first glass phase matrixwith a second glass phase matrix to form a multiphase glass slurry,applying the multiphase glass slurry to an outer surface of acarbon-carbon composite structure, and heating the carbon-carboncomposite structure to a temperature sufficient to adhere the multiphaseglass slurry to the carbon-carbon composite structure. The first glassphase matrix may be represented by the formulaa(A′₂O)_(x)(P₂O₅)_(y1)b(G_(f)O)_(y2)c(A″O)_(z): A′ is selected from:lithium, sodium, potassium, rubidium, cesium, and mixtures thereof;G_(f) is selected from: boron, silicon, sulfur, germanium, arsenic,antimony, and mixtures thereof, A″ is selected from: vanadium, aluminum,tin, titanium, chromium, manganese, iron, cobalt, nickel, copper,mercury, zinc, thulium, lead, zirconium, lanthanum, cerium,praseodymium, neodymium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, actinium, thorium,uranium, yttrium, gallium, magnesium, calcium, strontium, barium, tin,bismuth, cadmium, and mixtures thereof, a is a number in the range from1 to about 5; b is a number in the range from 0 to about 10; c is anumber in the range from 0 to about 30; x is a number in the range fromabout 0.050 to about 0.500; y₁ is a number in the range from about 0.040to about 0.950; y₂ is a number in the range from 0 to about 0.20; and zis a number in the range from about 0.01 to about 0.5; (x+y₁+y₂+z)=1;and x<(y₁+y₂) The second glass phase matrix may be a sealing glass. Themethod may further comprise prior to applying the multiphase glassslurry to the carbon-carbon composite structure, a pretreatingcomposition is applied to the outer surface of the carbon-carboncomposite structure, the pretreating composition comprising at least oneof a phosphoric acid, an acid phosphate salt, an aluminum salt, and anadditional salt, the carbon-carbon composite structure being porous, andthe pretreating composition penetrating at least some of a plurality ofpores of the carbon-carbon composite structure. The step of applying themultiphase glass slurry on the outer surface of the carbon-carboncomposite structure may comprise spraying or brushing the multiphaseglass slurry on the carbon-carbon composite structure. The first glassphase matrix may comprise between about 5% by weight and about 15% byweight of ammonium dihydrogen phosphate. The carbon-carbon compositestructure may comprise a component of an aircraft wheel brakingassembly. The multiphase glass slurry may comprise between about 1% byweight and about 15% by weight of the second glass phase matrix

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements.

FIG. 1A illustrates a cross sectional view of an aircraft wheel brakingassembly, in accordance with various embodiments;

FIG. 1B illustrates a partial side view of an aircraft wheel brakingassembly, in accordance with various embodiments; and

FIG. 2 illustrates a method for liming a catalytic oxidation reaction ina composite substrate in accordance with various embodiments.

DETAILED DESCRIPTION

The detailed description of embodiments herein makes reference to theaccompanying drawings, which show embodiments by way of illustration.While these embodiments are described in sufficient detail to enablethose skilled in the art to practice the inventions, it should beunderstood that other embodiments may be realized and that logical andmechanical changes may be made without departing from the spirit andscope of the inventions. Thus, the detailed description herein ispresented for purposes of illustration only and not for limitation. Forexample, any reference to singular includes plural embodiments, and anyreference to more than one component or step may include a singularembodiment or step. Also, any reference to attached, fixed, connected orthe like may include permanent, removable, temporary, partial, fulland/or any other possible attachment option.

With initial reference to FIGS. 1A and 1B, an aircraft wheel brakingassembly 10 in accordance with various embodiments is illustrated.Aircraft wheel braking assembly may, for example, comprise a bogie axle12, a wheel 14 including a hub 16 and a wheel well 18, a web 20, atorque take-out assembly 22, one or more torque bars 24, a wheelrotational axis 26, a wheel well recess 28, an actuator 30, multiplebrake rotors 32, multiple brake stators 34, a pressure plate 36, an endplate 38, a heat shield 40, multiple heat shield segments 42, multipleheat shield carriers 44, an air gap 46, multiple torque bar bolts 48, atorque bar pin 50, a wheel web hole 52, multiple heat shield fasteners53, multiple rotor lugs 54, and multiple stator slots 56. FIG. 1Billustrates a portion of wheel braking assembly 10 as viewed into wheelwell 18 and wheel well recess 28.

In various embodiments, the various components of wheel braking assembly10 may be subjected to the application of compositions and methods forprotecting the components from oxidation.

Brake disks (e.g., brake rotors 32 and stators 34) are disposed in wheelwell recess 28 of wheel well 18. Rotors 32 are secured to torque bars 24for rotation with wheel 14, while stators 34 are engaged with torquetake-out assembly 22. At least one actuator 30 is operable to compressrotors 32 and stators 34 for stopping the aircraft. In this example,actuator 30 is shown as a hydraulically actuated piston, but many typesof actuators are suitable, such as an electromechanical actuator.Pressure plate 36 and end plate 38 are disposed at opposite ends ofrotors 32 and stators 34. Rotors 32 and stators 34 can comprise anymaterial suitable for friction disks, including ceramics or carbonmaterials, such as a carbon/carbon composite.

Through compression of rotors 32 and stators 34 between pressure plate36 and end plate 38, the resulting frictional contact slows rotation ofwheel 14. Torque take-out assembly 22 is secured to a stationary portionof the landing gear truck such as a bogie beam or other landing gearstrut, such that torque take-out assembly 22 and stators 34 areprevented from rotating during braking of the aircraft.

Carbon-carbon composites in the friction disks may operate as a heatsink to absorb large amounts of kinetic energy converted to heat duringslowing of the aircraft. Heat shield 40 may reflect thermal energy awayfrom wheel well 18 and back toward rotors 32 and stators 34. Withreference to FIG. 1A, a portion of wheel well 18 and torque bar 24 isremoved to better illustrate heat shield 40 and heat shield segments 42.With reference to FIG. 1B, heat shield 40 is attached to wheel 14 and isconcentric with wheel well 18. Individual heat shield segments 42 may besecured in place between wheel well 18 and rotors 32 by respective heatshield carriers 44 fixed to wheel well 18. Air gap 46 is definedannularly between heat shield segments 42 and wheel well 18.

Torque bars 24 and heat shield carriers 44 can be secured to wheel 14using bolts or other fasteners. Torque bar bolts 48 can extend through ahole formed in a flange or other mounting surface on wheel 14. Eachtorque bar 24 can optionally include at least one torque bar pin 50 atan end opposite torque bar bolts 48, such that torque bar pin 50 can bereceived through wheel web hole 52 in web 20. Heat shield segments 42and respective heat shield carriers 44 can then be fastened to wheelwell 18 by heat shield fasteners 53.

Under the operating conditions (e.g., high temperature) of wheel brakingassembly 10, carbon-carbon composites may be prone to material loss fromoxidation of the carbon matrix. For example, various carbon-carboncomposite components of wheel braking assembly may experience bothcatalytic oxidation and inherent thermal oxidation caused by heating thecomposite during operation. In various embodiments, composite rotors 32and stators 34 may be heated to sufficiently high temperatures that mayoxidize the carbon surfaces exposed to air. At elevated temperatures,infiltration of air and contaminants may cause internal oxidation andweakening, especially in and around brake rotor lugs 54 or stator slots56 securing the friction disks to the respective torque bar 24 andtorque take-out assembly 22. Because carbon-carbon composite componentsof wheel braking assembly 10 may retain heat for a substantial timeperiod after slowing the aircraft, oxygen from the ambient atmospheremay react with the carbon matrix and/or carbon fibers to acceleratematerial loss. Further, damage to brake components may be caused by theoxidation enlargement of cracks around fibers or enlargement of cracksin a reaction-formed porous barrier coating (e.g., a silicon-basedbarrier coating) applied to the carbon-carbon composite.

Elements identified in severely oxidized regions of carbon-carboncomposite brake components include potassium (K) and sodium (Na). Thesealkali contaminants may come into contact with aircraft brakes as partof cleaning or de-icing materials. Other sources include salt depositsleft from seawater or sea spray. These and other contaminants (e.g. Ca,Fe, etc.) can penetrate and leave deposits in pores of carbon-carboncomposite aircraft brakes, including the substrate and any reactionformed porous barrier coating. When such contamination occurs, the rateof carbon loss by oxidation can be increased by one to two orders ofmagnitude.

In various embodiments, components of wheel braking assembly 10 mayreach operating temperatures in the range from about 100° C. (212° F.)up to about 900° C. (1652° F.), wherein in this context, the term“about” means+/−10° C. However, it will be recognized that the oxidationprotection compositions and methods of the present disclosure may bereadily adapted to many parts in this and other braking assemblies, aswell as to other carbon-carbon composite articles susceptible tooxidation losses from infiltration of atmospheric oxygen and/orcatalytic contaminants.

With initial reference to FIG. 2, a method 200 for liming a catalyticoxidation reaction in a composite substrate in accordance with variousembodiments is illustrated. Method 200 may, for example, compriseforming a multiphase glass composition and applying the composition tonon-wearing surfaces of carbon-carbon composite brake components. Invarious embodiments, method 200 may be used on the back face of endplates 36, 38, an inner diameter (ID) surface of stators 34 includingslots 56, as well as outer diameter (OD) surfaces of rotors 32 includinglugs 54. The multiphase glass composition of method 200 may be appliedto preselected regions of a carbon-carbon composite that may beotherwise susceptible to oxidation. For example, aircraft brake disksmay have the multiphase glass composition applied on or proximate statorslots 56 and/or rotor lugs 54.

In various embodiments, method 200 may comprise an optional pretreatmentstep 210. Step 210 may, for example, comprise applying a firstpretreating composition to the outer surface of a carbon-carboncomposite, such as a component of aircraft wheel braking assembly 10. Invarious embodiments, the first pretreating composition comprises analuminum oxide in water. For example, the aluminum oxide may comprise anadditive, such as a nanoparticle dispersion of aluminum oxide (forexample, NanoBYK-3600®, sold by BYK Additives & Instruments). The firstpretreating composition may further comprise a surfactant or a wettingagent. The carbon-carbon composite may be porous, allowing thepretreating composition to penetrate at least some of the pores of thecarbon-carbon composite.

In various embodiments, after applying the first pretreatingcomposition, the component is heated to remove water and fix thealuminum oxide in place. For example, the component may be heatedbetween about 100° C. (212° F.) and 200° C., and further, between 100°C. (212° F.) and 150° C. (392° F.).

Pretreatment step 210 may further comprise applying a second pretreatingcomposition. In various embodiments, the second pretreating compositioncomprises a phosphoric acid and an aluminum phosphate, aluminumhydroxide, or aluminum oxide. The second pretreating composition mayfurther comprise, for example, a second metal salt such as a magnesiumsalt. Further, the second pretreating composition may also comprise asurfactant or a wetting agent. In various embodiments, the secondpretreating composition is applied to the component atop the firstpretreating composition. The component may then, for example, be heated.In various embodiments, the component may be heated between about 600°C. (1112° F.) and about 800° C. (1472° F.), and further, between about650° C. (1202° F.) and 750° C. (1382° F.).

Method 200 may further comprise, for example, a step 220 of forming amultiphase glass slurry from a first glass phase matrix and a secondglass phase matrix. In various embodiments, step 220 comprises combiningthe first glass phase matrix and the second glass phase matrix with acarrier fluid (such as, for example, water) to form the multiphase glassslurry. To prepare the first glass phase matrix and the second glassphase matrix, one or both may be crushed or pulverized to form powdersor frits. The pulverized first glass phase matrix and/or pulverizedsecond glass phase matrix may be combined with the carrier fluid to formthe multiphase glass slurry.

The first glass matrix may, for example, comprise an acidic phosphateglass based on, for example, phosphorus pentoxide (P₂O₅). In variousembodiments, the first glass phase matrix may comprise one or morealkali metal glass modifiers, one or more glass network modifiers and/orone or more additional glass formers. Further, boron oxide or aprecursor may optionally be combined with the P₂O₅ mixture to form aborophosphate glass, which has improved self-healing properties at theoperating temperatures typically seen in aircraft braking assemblies. Invarious embodiments, the phosphate glass and/or borophosphate glass maybe characterized by the absence of an oxide of silicon. Further, theratio of P₂O₅ to metal oxide in the fused glass may be in the range fromabout 0.25 to about 5.

Potential alkali metal glass modifiers may be selected from oxides oflithium, sodium, potassium, rubidium, cesium, and mixtures thereof. Incertain embodiments, the glass modifier may be an oxide of lithium,sodium, potassium, or mixtures thereof. These or other glass modifiersmay function as fluxing agents. Additional glass formers can includeoxides of boron, silicon, sulfur, germanium, arsenic, antimony, andmixtures thereof. Further, in various embodiments, the first glass phasematrix may also comprise ammonium dihydrogen phosphate or monobasicammonium phosphate.

Suitable glass network modifiers include oxides of vanadium, aluminum,tin, titanium, chromium, manganese, iron, cobalt, nickel, copper,mercury, zinc, thulium, lead, zirconium, lanthanum, cerium,praseodymium, neodymium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, actinium, thorium,uranium, yttrium, gallium, magnesium, calcium, strontium, barium, tin,bismuth, cadmium, and mixtures thereof.

The first glass phase matrix may be prepared by combining the aboveingredients and heating them to a fusion temperature. In certainembodiments, depending on the particular combination of elements, thefusion temperature can be in the range from about 700° C. (1292° F.) toabout 1500° C. (2732° F.), wherein in this context, the term “about”means+/−10° C. The melt may then be cooled and pulverized to form thefrit. In various embodiments, the first glass phase matrix may beannealed to a rigid, friable state prior to being pulverized. Glasstransition temperature (T_(g)), glass softening temperature (T_(s)) andglass melting temperature (T_(m)) may be increased by increasingrefinement time and/or temperature. Before fusion, the first glass phasematrix comprises from about 20 mol % to about 80 mol % of P₂O₅, whereinthe term “about” means+/−0.5 mol %. In various embodiments, the firstglass phase matrix comprises from about 30 mol % to about 70 mol % P₂O₅,or precursor thereof. In various embodiments, the first glass phasematrix comprises from about 40 to about 60 mol % of P₂O₅. The firstglass phase matrix can comprise from about 5 mol % to about 50 mol % ofthe alkali metal oxide. In various embodiments, the first glass phasematrix comprises from about 10 mol % to about 40 mol % of the alkalimetal oxide. Further, the first phosphate glass composition matrixcomprises from about 15 to about 30 mol % of the alkali metal oxide orone or more precursors thereof. In various embodiments, the first glassphase matrix can comprise from about 0.5 mol % to about 50 mol % of oneor more of the above-indicated glass formers. The first glass phasematrix may comprise about 5 to about 20 mol % of one or more of theabove-indicated glass formers.

In various embodiments, the first glass phase matrix can comprise fromabout 0.5 mol % to about 40 mol % of one or more of the above-indicatedglass network modifiers. The first glass phase matrix may comprise fromabout 2.0 mol % to about 25 mol % of one or more of the above-indicatedglass network modifiers.

In various embodiments, the first glass phase matrix may represented bythe formula:

a(A′₂O)_(x)(P₂O₅)_(y1)b(G_(f)O)_(y2)c(A″O)_(z)  [1]

In Formula 1, A′ is selected from: lithium, sodium, potassium, rubidium,cesium, and mixtures thereof. G_(f) is selected from: boron, silicon,sulfur, germanium, arsenic, antimony, and mixtures thereof. A″ isselected from: vanadium, aluminum, tin, titanium, chromium, manganese,iron, cobalt, nickel, copper, mercury, zinc, thulium, lead, zirconium,lanthanum, cerium, praseodymium, neodymium, samarium, europium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium,actinium, thorium, uranium, yttrium, gallium, magnesium, calcium,strontium, barium, tin, bismuth, cadmium, and mixtures thereof. a is anumber in the range from 1 to about 5. b is a number in the range from 0to about 10. c is a number in the range from 0 to about 30. x is anumber in the range from about 0.050 to about 0.500. y₁ is a number inthe range from about 0.040 to about 0.950. y₂ is a number in the rangefrom 0 to about 0.20. z is a number in the range from about 0.01 toabout 0.5. In addition, with regard to the individual variables,(x+y₁+y₂+z)=1, and x<(y₁+y₂). The first glass phase matrix may beformulated to balance the reactivity, durability and flow of theresulting multiphase slurry for optimal performance.

In various embodiments, the second glass phase matrix may be a sealingglass, such as the sealing glasses described in Table 1 below.

TABLE 1 Second Glass Density Soft. Pt. CTE Phase Matrix (g/cc) (° C.)(ppm/° C. T_(g) (° C.) T_(s) (° C.) A 2.99 395 21.6 318 348 B 6.79 40810.5 324 455 C 2.96 422 20.0 350 380 D 5.73 490 8.2 411 452 E 2.34 5909.4 465 N/A F 3.32 622 5.8 460 524 G 2.61 639 9.3 487 537 H 3.14 648 4.0539 598 I 2.59 654 10.0 481 559 J 3.03 658 8.7 589 625 K 2.25 673 5.7577 629 L 2.41 680 5.0 505 N/A M 2.66 699 7.2 613 635 N 2.91 717 3.1 575620 O 2.33 717 4.3 N/A N/A P 2.34 719 4.7 544 613 Q 2.55 726 5.9 650 696R 2.72 862 5.2 717 784

For example, the second glass phase matrix may comprise one of glassmatrices A-R of Table 1. In various embodiments, the second glass phasematrix comprises a sealing glass having a glass transition temperaturehigher than the first glass phase matrix. For example, the glasstransition temperature of the second glass phase matrix may be at leastabout 100° C. higher than the glass transition temperature of the firstglass phase matrix.

As illustrated in Table 2 below, in various embodiments, the multiphaseglass slurry may comprise a greater amount of the first glass phasematrix than the second glass phase matrix.

TABLE 2 Weight % of Various Components of Various Multiphase GlassSlurries Component MP1 MP2 MP3 MP4 MP5 First Glass Phase Matrix 35 35 3535 35 Second Glass Phase Matrix 1 1 1 2 4 Ammonium Dihydrogen 10 10 1010 10 Phosphate Water 50 50 50 50 50

In various embodiments, the amount of second glass phase matrix in themultiphase glass slurry may vary from about 1% by weight to about 15% byweight. Further, in various embodiments, the multiphase glass slurry maycomprise between about 5% by weight and about 15% by weight of ammoniumdihydrogen phosphate. In this context, “about” means+/−0.5% by weight

The multiphase glass slurry offers improved oxidation protection overprior art oxidation protection systems. For example, the differencebetween the first transition temperature (of the first glass phase) andthe second transition temperature (of the second glass phase) mayprovide enhanced resistance to migration at high temperatures, which inturn may reduce oxidation damage to the carbon-carbon compositestructure.

In various embodiments, method 200 further comprises a step 230 ofapplying the multiphase glass slurry to the carbon-carbon compositestructure. Step 230 may comprise, for example, spraying or brushing themultiphase glass slurry on to the outer surface of the carbon-carboncomposite structure. In various embodiments, step 230 may compriseapplying the multiphase glass slurry on to the outer surface of thecarbon-carbon composite structure via chemical vapor deposition. Anysuitable manner of applying the multiphase glass slurry to thecarbon-carbon composite is within the scope of the present disclosure.

In various embodiments, method 200 further comprises a step 240 ofheating the carbon-carbon composite structure to adhere the multiphaseglass slurry to the carbon-carbon composite structure. The treatedcarbon-carbon composite may be heated (e.g., dried or baked) at atemperature in the range from about 200° C. (392° F.) to about 1000° C.(1832° F.), wherein the term “about” means+/−10° C. In variousembodiments, the composite is heated to a temperature in a range fromabout 600° C. (1112° F.) to about 1000° C. (1832° F.), or between about200° C. (392° F.) to about 900° C. (1652° F.), or further, between about400° C. (752° F.) to about 850° C. (1562° F.).

Step 240 may, for example, comprise heating the carbon-carbon compositestructure for a period between about 0.5 hour and about 8 hours, whereinin this context, “about” means+/−0.5 hours.

In various embodiments, the composite may be heated to a first, lowertemperature (for example, about 30° C. (86° F.) to about 300° C. (572°F.), wherein the term “about” means+/−10° C.) to bake or dry themultiphase glass slurry at a controlled depth. A second, highertemperature (for example, about 300° C. (572° F.) to about 1000° C.(1832° F.)) may then be used to form a deposit from the base layerwithin the pores of the carbon-carbon composite. The duration of eachheating step can be determined as a fraction of the overall heating timeand can range from about 10% to about 50%. In various embodiments, theduration of the lower temperature heating step(s) can range from about20% to about 40% of the overall heating time. The lower temperaturestep(s) may occupy a larger fraction of the overall heating time, forexample, to provide relatively slow heating up to and through the firstlower temperature. The exact heating profile will depend on acombination of the first temperature and desired depth of the dryingportion.

Step 240 may be performed in an inert or substantially environment, suchas under a blanket of inert gas (e.g., nitrogen, argon, and the like).For example, a carbon-carbon composite may be pretreated or warmed priorto application of the multiphase glass slurry to aid in the penetrationof the slurry. Step 240 may be for a period of about 2 hours at atemperature of about 750° C. (1382° F.) to about 800° C. (1472° F.),wherein the term “about” means+/−10° C. The carbon-carbon composite andmultiphase glass slurry may then be dried or baked in a non-oxidizing,inert atmosphere, e.g., nitrogen (N₂), to optimize the retention of themultiphase glass slurry in the pores. This retention may, for example,be improved by heating the carbon-carbon composite to about 200° C.(392° F.) and maintaining the temperature for about 1 hour beforeheating the carbon-carbon composite to a temperature in the rangedescribed above. The temperature rise may be controlled at a rate thatremoves water without boiling, and provides temperature uniformitythroughout the carbon-carbon composite.

Benefits and other advantages have been described herein with regard tospecific embodiments. Furthermore, the connecting lines shown in thevarious figures contained herein are intended to represent exemplaryfunctional relationships and/or physical couplings between the variouselements. It should be noted that many alternative or additionalfunctional relationships or physical connections may be present in apractical system. However, the benefits, advantages, solutions toproblems, and any elements that may cause any benefit, advantage, orsolution to occur or become more pronounced are not to be construed ascritical, required, or essential features or elements of the disclosure.The scope of the disclosure is accordingly to be limited by nothingother than the appended claims, in which reference to an element in thesingular is not intended to mean “one and only one” unless explicitly sostated, but rather “one or more.” Moreover, where a phrase similar to“at least one of A, B, or C” is used in the claims, it is intended thatthe phrase be interpreted to mean that A alone may be present in anembodiment, B alone may be present in an embodiment, C alone may bepresent in an embodiment, or that any combination of the elements A, Band C may be present in a single embodiment; for example, A and B, A andC, B and C, or A and B and C.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment,” “an embodiment,” “anexample embodiment,” etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112(f), unless the element is expressly recitedusing the phrase “means for.” As used herein, the terms “comprises,”“comprising,” or any other variation thereof, are intended to cover anon-exclusive inclusion, such that a process, method, article, orapparatus that comprises a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus.

What is claimed is:
 1. An article comprising: a carbon-carbon compositestructure; and a multiphase oxidation protection composition including afirst glass phase and a second glass phase on an outer surface of thecarbon-carbon composite structure, wherein the first glass phasecomprises a phosphate glass composition having a first transitiontemperature, wherein the second glass phase comprises a secondtransition temperature higher than the first transition temperature, andwherein the second transition temperature is at least 100° C. higherthan the first transition temperature.
 2. The article of claim 1,wherein the second glass phase comprises a sealing glass.
 3. The articleof claim 1 wherein the first glass phase is represented by the formulaa(A′₂O)_(x)(P₂O₅)_(y1)b(G_(f)O)_(y2)c(A″O)_(z): A′ is selected from:lithium, sodium, potassium, rubidium, cesium, and mixtures thereof;G_(f) is selected from: boron, silicon, sulfur, germanium, arsenic,antimony, and mixtures thereof; A″ is selected from: vanadium, aluminum,tin, titanium, chromium, manganese, iron, cobalt, nickel, copper,mercury, zinc, thulium, lead, zirconium, lanthanum, cerium,praseodymium, neodymium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, actinium, thorium,uranium, yttrium, gallium, magnesium, calcium, strontium, barium, tin,bismuth, cadmium, and mixtures thereof; a is a number in the range from1 to about 5; b is a number in the range from 0 to about 10; c is anumber in the range from 0 to about 30; x is a number in the range fromabout 0.050 to about 0.500; y₁ is a number in the range from about 0.040to about 0.950; y₂ is a number in the range from 0 to about 0.20; and zis a number in the range from about 0.01 to about 0.5; (x+y₁+y₂+z)=1;and x<(y₁+y₂).
 4. The article of claim 3, wherein the multiphase glassslurry comprises between about 5% by weight and about 15% by weight ofammonium dihydrogen phosphate.
 5. The article of claim 1, wherein themultiphase oxidation protection composition comprises between about 1%by weight and about 15% by weight of the second glass phase.
 6. Thearticle of claim 1, wherein the article comprises a component of anaircraft wheel braking assembly.
 7. The article of claim 1, wherein thesecond glass phase comprises at least one of a first sealing glasshaving a density of 2.99 grams per cubic centimeter (g/cc), a softeningpoint of 395° C., a coefficient of thermal expansion of 21.6 ppm/° C.,and a transition temperature of 318° C.; a second sealing glass having adensity of 6.79 g/cc, a softening point of 408° C., a coefficient ofthermal expansion of 10.5 ppm/° C., and a transition temperature of 324°C.; a third sealing glass having a density of 2.96 g/cc, a softeningpoint of 422° C., a coefficient of thermal expansion of 20 ppm/° C., anda transition temperature of 350° C.; a fourth sealing glass having adensity of 5.73 g/cc, a softening point of 490° C., a coefficient ofthermal expansion of 8.2 ppm/° C., and a transition temperature of 411°C.; a fifth sealing glass having a density of 2.34 g/cc, a softeningpoint of 590° C., a coefficient of thermal expansion of 9.4 ppm/° C.,and a transition temperature of 465° C.; a sixth sealing glass having adensity of 3.32 g/cc, a softening point of 622° C., a coefficient ofthermal expansion of 5.8 ppm/° C., and a transition temperature of 460°C.; a seventh sealing glass having a density of 2.61 g/cc, a softeningpoint of 639° C., a coefficient of thermal expansion of 9.3 ppm/° C.,and a transition temperature of 487° C.; an eighth sealing glass havingan density of 3.14 g/cc, an softening point of 648° C., an coefficientof thermal expansion of 4 ppm/° C., and an transition temperature of539° C.; a ninth sealing glass having a density of 2.59 g/cc, asoftening point of 654° C., a coefficient of thermal expansion of 10ppm/° C., and a transition temperature of 481° C.; a tenth sealing glasshaving a density of 3.03 g/cc, a softening point of 658° C., acoefficient of thermal expansion of 8.7 ppm/° C., and a transitiontemperature of 589° C.; an eleventh sealing glass having an density of2.25 g/cc, an softening point of 673° C., an coefficient of thermalexpansion of 5.7 ppm/° C., and an transition temperature of 577° C.; atwelfth sealing glass having a density of 2.41 g/cc, a softening pointof 680° C., a coefficient of thermal expansion of 5 ppm/° C., and atransition temperature of 505° C.; a thirteenth sealing glass having adensity of 2.66 g/cc, a softening point of 699° C., a coefficient ofthermal expansion of 7.2 ppm/° C., and a transition temperature of 613°C.; a fourteenth sealing glass having a density of 2.91 g/cc, asoftening point of 717° C., a coefficient of thermal expansion of 3.1ppm/° C., and a transition temperature of 575° C.; a fifteenth sealingglass having a density of 2.33 g/cc, a softening point of 717° C., and acoefficient of thermal expansion of 4.3 ppm/° C.; a sixteenth sealingglass having a density of 2.34 g/cc, a softening point of 719° C., acoefficient of thermal expansion of 4.7 ppm/° C., and a transitiontemperature of 544° C.; a seventeenth sealing glass having a density of2.55 g/cc, a softening point of 726° C., a coefficient of thermalexpansion of 5.9 ppm/° C., and a transition temperature of 650° C.; oran eighteenth sealing glass having an density of 2.72 g/cc, an softeningpoint of 862° C., an coefficient of thermal expansion of 5.2 ppm/° C.,and an transition temperature of 717° C.